Integrated circuit (IC) packages generally contain integrated circuit chips or die-containing densely packed circuits. Electronic circuits placed in close proximity to each other on an integrated circuit die can cause electromagnetic interference. That is, the electric signals, whether intentional or not (noise), can propagate to an adjacent or remote circuit element on the same die and interfere with the operation of that circuit or superimpose upon the signal being generated in the adjacent or remote circuit element. As circuit miniaturization progresses, interference between circuits within a same integrated circuit die sometimes occurs. Moreover, as those circuits get closer and closer, the problem becomes more common place especially in the context of high performance RF or analog signals where signal fidelity is of great importance. The substrate of the die hosting the circuit can, in fact, serve as a conduit for the passage of noise.
In the area of analogue signal amplification and conditioning this is an important concern. As the power of a signal generated and propagating within an IC increases, its ability to cause noise in other signals also increases. Whereas for digital circuits this noise may be manageable, in analogue circuitry, noise is considered highly undesirable. It is therefore desirous to prevent circuits within an integrated circuit from unintentionally dispersing signals into adjacent circuits within a same die.
A transmission line can be considered an adjacent or remote circuit that can be compromised by the presence of noise in the underlying substrate. A transmission line must be isolated from the effect of the signals and/or noise generated in the adjacent circuits sharing the same die in order to preserve the signal on the transmission line. Having a means to suppress the addition of noise signals onto the intended transmission line signal is highly desirable especially in the context of circuits which feature power amplifier stages adjacent to analog or RF signal receivers.
The interference problem is a particular problem at high frequencies (HF) and radio frequencies (RF), though electromagnetic interference between circuits on an integrated circuit can also be a problem at lower frequencies. Radiation or other energy is often disbursed by substrate coupling, through common ground, through common power supplies or through transmission line effects.
Heretofore, electromagnetic interference between circuitry has been prevented by limiting the number of systems or circuits on a chip or die. Each die or chip is generally associated with a single circuit that is a source or is sensitive to electromagnetic radiation. Typically, each chip is packaged and that package may be externally shielded, such as, in a Faraday cage.
Limiting the number of circuits on the chip, however, increases costs of the entire system because the system must then employ more chips to achieve the same functionality. In addition, the use of individual Faraday cages for each package may increase the cost of the system. Furthermore, shielding each chip also increases manufacturing and assembly costs along with the fact that the entire size of the system is increased by the increased number of packaged chips and the external Faraday shielding.
An example of conventional electromagnetic shielding techniques is disclosed in U.S. Pat. No. 5,986,340, which describes a ball grid array (BGA) package. The package includes an external Faraday cage formed around the integrated circuit die. The external Faraday cage is comprised of a heat sink surrounding the integrated circuit die and a metal plate on an upper peripheral surface of the heat sink.
U.S. Pat. No. 5,986,340 is similar to U.S. Pat. No. 5,955,789 and discloses a plastic ball grid array (BGA) electronic package in a cavity down configuration. The package includes an active element mounted on a package substrate and is for use in HF applications. An external Faraday cage is realized to protect the active element from external HF interferences. A row of solder balls connected in a zig-zag fashion on a bottom of the package substrate and plated-through holes through the package substrate form lateral sides of the external Faraday cage. The top-side of the external Faraday cage is formed of a metal cap and the bottom side of the external Faraday cage is formed by a ground plane of the main board. The package in U.S. Pat. No. 5,955,789, however, does not provide shielding within the integrated circuit (IC) die.
U.S. Pat. No. 7,151,011 teaches a method of forming a Faraday cage partially integrated within an integrated circuit using vias as a set of vertical bars forming a cage with a solid roof and floor to shield a portion of the circuit from an inductive element on the top metal layer of the integrated circuit. For example, the vias form a cage around the inductor with an external metal layer shielding the inductor from external radiation and a metal layer within the integrated circuit close to the doped layer shields the doped layer. Unfortunately, such an arrangement has several drawbacks. Firstly, it allows interference signals to propagate within metal layers near the inductor. These signals are then capable of interfering with circuit functionality. Secondly, the method set out in U.S. Pat. No. 7,151,011 is only capable of shielding portions of the circuit within the metalized layers from the semiconductor substrate. This is not useful when RF analogue signals are being manipulated, for example amplified, using transistors and other components relying on semiconductors.
Of course, the proposed configuration in U.S. Pat. No. 7,151,011 is for shielding inductors formed exclusively within the metal layers of a semiconductor integrated circuit. It is suggested that a further ground plane, for example in the packaging, disposed adjacent the layer with the inductor be used to complete the shielding. This effectively limits the shielding capabilities significantly rendering them well suited for some applications and poorly suited for others.
One such other application is RF transceiver circuits for receiving and/or transmitting more than one signal. Such a circuit comprises a plurality of RF paths each of which can interfere with the other RF paths and each of which can be interfered with.
It would be advantageous to overcome at least some of the limitations of the prior art.